The use of volume-limited medical ventilators for providing a patient with breathing gas having a set oxygen concentration and tidal volume is shown for example, by U.S. Pat. No. 3,831,595, granted Aug. 27, 1974 to Valenta et al, and assigned to the same assignee as the present invention. In the use of such ventilators, the patient's treatment may sometimes call for the addition of a prescribed drug or medicine to the gas in the breathing circuit. Heretofore, it has been customary to administer the medicine or drug by means of an electrically operated auxiliary control system including a drug nebulizer connected to the breathing circuit and powered by a continuously running motor-driven compressor. However, electrical systems of such character when used with medical ventilators as described above, have significant disadvantages; for example, it is highly desirable from the safety standpoint that any electrical components or electrical connections which can be hazardous in the presence of oxygen, or oxygen-rich gases, be entirely eliminated from the equipment. Furthermore, the auxiliary electrical motor-compressor equipment requires a back-up source of electricity and is comparatively expensive.
In a known form of medical ventilator system for introducing medication by pneumatic nebulizing action, a combined humidifier and drug nebulizer unit is series-connected directly in the gas supply circuit leading to a main gas dispensing and measuring chamber for the breathing circuit. This arrangement is unsatisfactory as it creates problems such as contamination, due to condensation of drug-laden moisture in the measuring chamber during passage of the humidified gas therethrough to the breathing circuit. Accordingly, a sterilizing operation is required to clean the chamber, etc. after each patient-treatment.
In brief, drug nebulizing systems for medical ventilators such as described above, have been found unsatisfactory in practice for the reasons indicated, especially where an automatic, reliable, safe and clean system is desired for adding medication to the patient's breathing circuit.
The present invention therefore aims to provide an improved system and apparatus for overcoming disadvantages of the character described above, in the use of drug nebulizing means in volume-limited medical ventilator systems.